As you may notice, 5d^9 should be 5d^10. But my teacher taught us that you have to reduce the number if you think it is closer and she added that if you go more, the answer will be greater. So just minus, at least. She said.

Now, I really cannot understand this. Would somebody give me a quiz and wait me to see if my answer is correct?

Any help will be greatly appreciated and sorry for the bad explanation, if ever.

In general the number of electrons should match the protons. On of the things that make metals is their outer electrons tend to float, they drift around a bit. It is also what makes metals conductive, this ability to pass electrons around.

Insulators are just the opposite, they do not share electrons well, the electrons are bound tightly to the outer shells.

In general the number of electrons should match the protons. On of the things that make metals is their outer electrons tend to float, they drift around a bit. It is also what makes metals conductive, this ability to pass electrons around.

Insulators are just the opposite, they do not share electrons well, the electrons are bound tightly to the outer shells.

It is also a large part of what drives chemistry.

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So for example I encountered an element which has a number of 86 protons. Just for example. So my electron configuration should be like this?